A Medium Voltage Circuit Breaker that has at least a pair of contact mutually coupleable and uncoupleable to carry out an opening/closing operation, a magnetic actuator operatively connected to at least one of the contacts, and a capacitor bank that has one or more capacitors that deliver power to the magnetic actuator for carrying out the opening/closing operation and a control device. The Medium Voltage Circuit Breaker further has a supervisor device of the capacitor bank which measures the Equivalent Series Resistance and/or the Capacitance of the capacitor bank system.